Abstract
Slagging and fouling are common problems associated with biomass firing. The different nature of the mineral and phase composition of biomass ash makes the vast experience with coal firing insufficient for its translation to biomass fuels, especially when it comes to slagging and fouling behavior. Biomass tends to have lower ash content than coals; however, it is often rich in volatile alkalis. The mineral deposits found on boiler walls and superheater tubes are often comprised of alkali compounds. Numerous studies on ash melting and particle sticking behavior have been conducted. Laboratory observed ash fusion temperatures are commonly used to evaluate the slagging and fouling propensity of fuels. The tests are often time consuming, therefore several predictive indices have been developed to estimate the propensity based on the ash composition alone. Thermodynamic models as well as neural networks have also been applied to this end. However, for practical in the field purposes, the ash fusion tests and predictive indices are preferred because of their convenience. An overview of these indices is presented in this work. A sizeable dataset has been collected in order to statistically evaluate the applicability of the indices and of several AFT prediction formulas. General trends in ash composition on this extensive dataset have also been illustrated. Finally, a more convenient graphical solution is presented for preliminary slagging and fouling predictions.
Highlights
With the growing demand for renewable energy sources, biomass and derived biofuels have been gaining increasing interest
The initial deformation temperature (IDT) of the original standard has been replaced by the SST, which is defined as the temperature at which the area of the test piece falls below 95% of the original area due to shrinking of the test piece
The diagram was further divided into three distinct regions based on the prevalent IDT group found within them: Region (1): samples found within this region show high IDTs and should cause little to no fouling problems when burnt at common flame temperatures
Summary
With the growing demand for renewable energy sources, biomass and derived biofuels have been gaining increasing interest. Ash de posits form both inside the furnace as well as on the adjacent heat ex changers, e.g. superheater tubes These agglomerates hinder the effectiveness of the heat exchanger and directly influence high tem perature chlorine induced corrosion by creating a reducing atmosphere on the surface of the tubes [1]. This can lead to unscheduled plant shutdowns due to mechanical failures. Agglomerates, typical for wood combustion, impact the walls or tubes and rearrange their structure During this process, they dissipate all kinetic energy, which leads to the particle sticking to the surface rather than rebound ing. Fuels with high ash fusion temperatures (AFTs) are preferred
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